Practical benchmark
With 8% waste, a 30 L keg gives about 27.6 L. At 400 ml per glass, that is roughly 69 sellable serves.
Beer
Keg yield depends on litres, pour size, foam loss and line waste. A 30 L keg rarely gives 30 L of sellable beer.
With 8% waste, a 30 L keg gives about 27.6 L. At 400 ml per glass, that is roughly 69 sellable serves.
Once you know real yield, divide keg cost by sellable serves to price each glass with a sustainable margin.
Counting glasses on nominal litres, forgetting line cleaning and the first purge, and applying one cost per serve across different glass sizes all overstate real yield.
Foam, the initial purge and imperfect pouring remove sellable beer. A poorly set system can push losses well beyond 10%, so always price on real serves, not nominal litres.